This invention relates generally to lower leg prostheses and, more particularly, to lower leg prostheses configured to duplicate the dynamic performance characteristics of the human foot and ankle.
Significant advancements in the field of lower leg prostheses have been made in recent years, due largely to the development of composite materials technology. Lower leg prostheses incorporating fiberglass/epoxy and carbon fiber/epoxy composite materials have been developed, which closely duplicate the dynamic performance characteristics of the human foot and ankle.
One such lower leg prosthesis is disclosed in U.S. Pat. No. 4,959,073 issued to Merlette. The Merlette prosthesis incorporates an elongated composite main member having a leg section and a forwardly extending foot section, and it further incorporates a heel member projecting rearwardly from the underside of the main member""s foot section. A high-density polyurethane elastomer is disposed between the heel member and the main member""s foot section, to permanently attach the two members together and to provide limited cushioning. The upper end of the main member""s leg section supports an amputation socket for receiving the amputee""s residual limb, and a crepe sole can be attached to the underside of the heel member. A foam foot shell or cosmesis can be placed over the composite members, to provide the prosthesis with an appearance of a natural human foot.
The Merlette lower leg prosthesis described briefly above has enjoyed substantial commercial success. Nevertheless, it is believed that the Merlette prosthesis can be improved upon by modifying the structure that resists upward deflection of its heel section at heel strike and also by providing enhanced inversion/eversion compliance.
It should therefore be appreciated that there exists a need for a lower leg prosthesis that, during use, provides an improved dynamic feel at heel strike and that provides improved inversion/eversion compliance. The present invention fulfills this need and provides further related advantages.
The present invention is embodied in an improved lower leg prosthesis that, during use, provides an improved dynamic feel at heel strike and that provides improved inversion/eversion compliance. The prosthesis includes an elongated pylon having an upper, generally vertical section and a lower, forwardly oriented foot section, wherein the upper section defines a vertical pylon axis, and it further includes a generally horizontally oriented foot plate disposed beneath the pylon and including a heel section projecting a substantial distance rearwardly of the vertical pylon axis. The pylon and the foot plate both are formed of a high-strength composite material, e.g., an epoxy/carbon fiber composite material. Further, an elastomeric layer, e.g., formed of a high-density polyurethane material, is interposed between the pylon and the foot plate, extending along substantially the entire length of the heel section of the foot plate, for attaching the pylon and foot plate together. During use of the prosthesis, at heel strike, upward deflection of the foot plate""s heel section is limited in substantial part both by the stiffness of the heel section, itself, and by compression of the portion of the elastomeric layer disposed rearwardly of the vertical pylon axis.
In a more detailed feature of the invention, the forward tip of the foot plate is disposed substantially beneath the forward tip of the pylon""s forwardly oriented foot section, and the elastomeric layer extends along substantially the entire length of the foot plate, from its forward tip to the rearward tip. The elastomeric layer preferably has a width that tapers from a minimum at the foot plate""s forward tip to a maximum at a mid-portion of the foot plate to a minimum at the foot plate""s rearward tip. In addition, the pylon""s forwardly oriented foot section has a width that tapers from a maximum at a location substantially aligned with the maximum width of the elastomeric layer to a minimum at the foot section""s forward tip. The points of maximum width of the pylon""s forwardly oriented foot section and the elastomeric layer preferably are located forward of the vertical pylon axis.
In other more detailed features of the invention, the portion of the elastomeric layer disposed on the heel section of the foot plate has a concave upper surface. This concave upper surface preferably is a circular arc, substantially tangent both to the pylon""s upper, vertical section and to the foot plate""s rearward tip.
The portion of the elastomeric layer disposed rearwardly of the vertical pylon axis preferably provides at least about one-third of the total resistance to upward flexing of the foot plate""s heel section at heel strike. In addition, this layer has a thickness of at least about one-half centimeter along substantially its entire length.
Other features and advantages of the present invention should become apparent from the following description of the preferred embodiments, taken in conjunction with the exemplary drawings, which illustrate the principles of the invention.